The invention relates to a drive assembly with at least one constant velocity fixed joint and a set of rolling contact member guiding means.
Such constant velocity fixed joints comprise a hollow outer part, an inner part with an outer face received in the outer part, a cage arranged between the outer part and inner part and balls which are held by the cage in a common plane and which engage running grooves in an inner face of the hollow outer part and in the outer face of the inner part for the purpose of transmitting torque between the outer part and inner part. The outer part and the inner part only permit angular movements relative to one another around the articulation center. The rolling contact member guiding means allow the transmission of torque in the case of a setting movement along a setting axis. To achieve this objective, the rolling contact member guiding means comprise a plunging journal with inner grooves extending in the outer face of same parallel to the setting axis, as well as a plunging sleeve with a bore which is adjustably entered by the plunging journal with inner grooves extending in the outer face of same parallel to the setting axis. Also included is a plunging sleeve with a bore which is adjustably entered by the plunging journal along the setting axis. In the bore of the plunging sleeve, the inner grooves are arranged opposite outer grooves and extend parallel to the setting axis. Furthermore, there are provided guiding balls which are arranged in the respective opposed pairs of inner and outer groves. The guiding balls are held in a guiding cage.
Such an assembly is described in DE 44 19 373 A1. The plunging journal of the rolling contact member guiding means is produced so as to be integral with the inner part of the constant velocity joint. The inner part of the constant velocity fixed joint, in its outer face, is provided with inner running grooves which extend in an undercut-free way from a first open end of the outer part. Said inner running grooves are arranged opposite outer running grooves in the outer part which also start from the first open end in an undercut-free way. Furthermore, the cage is guided by means of a spherical inner face on a spherical outer face of the inner part. The inner part comprises a control face in the form of a hollow ball on which there is supported a control element with a spherical outer face. The control element itself is supported on a face of the supporting element which, in turn, is secured in the outer part. Between the outer face of the cage and the inner face of the outer part there is provided a distance. In the axial direction, the inner part is held and centered relative to the outer part by the balls and by the shape of the inner running grooves and outer running grooves on the one hand and by the control element in connection with the supporting element in the outer part on the other hand.
Such joints are mostly used in motor vehicles for transporting passengers or in delivery vans.
In the case of rear wheel drive vehicles or four wheel drive vehicles, the front gearbox output is connected to the rear axle drive by a propeller shaft. Especially in passenger cars with a rear wheel drive only, such propeller shafts rotate at high speeds up to 10,000 revolutions per minute. Such a propeller shaft usually comprises two shaft portions, with the first shaft portion being connected to the gearbox output of the front drive unit, with the outer end being held by an intermediate bearing. The second shaft portion, at one end, is connected to the drive input of the rear axle drive and by means of a joint it is connected to the first shaft portion in the region of the intermediate bearing. Normally, universal joints are arranged at the ends of the propeller shaft, i.e. toward the gearbox output and the axle drive input. A universal joint can also be provided in the central region. However, it is also known to use a constant velocity plunging joint in this central region, as described, for example, in the book by Prof. Dip.-Ing. Jornsen Reimpell: Fahrwerktechnik 1, 5.sup.th edition, Vogel-Verlag, p. 285, FIG. 3.1/21.
DE 40 31 820 C2 describes a constant velocity fixed joint whose outer part comprises a first and a second open end. It comprises a cavity which is centered on the longitudinal outer part axis. The first outer running grooves start from the first open end and extend towards the second open end. The second outer running grooves start from the second open end and extend towards the first open end.
All outer running grooves extend in a curve-like and undercut-free way from the respective end from which they start. In the cavity of the outer part, there is arranged an inner part. The inner part comprises a longitudinal inner part axis and a spherical outer face provided with first and second inner running grooves which are positioned opposite the first and second outer running grooves and, with reference to the inner part axis, extend in meridian planes.
The first inner running grooves are arranged opposite the first outer grooves, while starting from the first open end, extending towards the second open end in a curve-like and undercut-free way. The second inner running grooves are arranged opposite the second outer running grooves, which, together, form pairs, with the second inner running grooves starting from the second open end and extending curve-like and in an undercut-free way towards the first open end. Between the inner face of the outer part and the spherical outer face of the inner part, there is arranged a cage whose spherical outer face is arranged with play relative to the inner face of the outer part. The cage comprises a cylindrical bore which is held with play relative to the spherical outer face of the inner part. The cage is provided with radial apertures which are arranged in accordance with the pairs of inner running grooves and outer running grooves, which form windows and guide the balls between the lateral guiding faces. For the purpose of transmitting torque, the balls engage between the outer part and inner part into the outer running grooves and inner running grooves associated with pairs. The centers of all balls are held in one plane which contains the window centers between the lateral guiding faces. The cage is centered by the balls only. In constant velocity joints rotating at high speeds such as they are used for example in the propeller shaft for transmitting a rotational movement in passenger cars from its front drive unit to the rear axle drive in rear wheel drive vehicles, such a design is disadvantageous. There occur vibrations because the center of gravity of the cage is displaced, so that the centrifugal force comes into effect.
In such joints, under torque conditions, the forces applied by the pairs of running grooves extending in opposite directions to the balls are accommodated by the cage. In the process, smooth and low-friction running conditions may be interfered with by external forces in that there occurs an axial displacement of the inner part and outer part. The cage is additionally loaded by such forces on one side, thus causing out-of-balance. The cage is subject to higher forces.